Temperature dependence of the emittance of LiF and LiNbO3 in the near-infrared spectra

This study investigates the temperature dependence of the normal emittance in 3-5, 5, 10.6 and 8-12 mu m spectral ranee for LiNbO3 and LiF rods with both crystal and polycrystalline structures. According to the results, the normal emittance in the near-infrared spectra increases with increasing wavelength. The normal emittances at 10.6 and 8-12 mu m are not only invariant with temperature, but also exceed 0.9. When the temperature increases. the normal emittances at 3-5 and 5 mu m for the LiF single-crystal rod continuously increase regardless of the phase change from the solid state to the liquid state. Before the temperature reaches the Curie point, the normal emittances at 3-5 and 5 mu m for the LiNbO3 single-crystal I od increase with increasing temperature. The normal emittances at 3-5 and 5 mu m then decrease as the temperature further increases. A significant decrease in the normal emittance at 3-5 and 5 mu m occurs when the emission is only from the melt. In addition. the magnitudes of the normal emittance at 3-5 and 5 mu m are enhanced by the scattering effect due to the porous structure of the solid.